A layer on top of the soil with a population of the supportive mite Tyrophagus putrescentiae could help the predatory mite to survive periods when thrips numbers are low. The colonisation by the supportive mite was investigated with layers of different materials like bran, wheat middlings, corn gluten, and several compost types. The best result was achieved with bran in combination with baker's yeast.

Questions before application on a practical scale included humidity (RH) requirements, and the density of the top layer. Tyrophagus putrescentiae seems to like high RH, but it couldn’t cope with drought. The lower limit lies somewhere between 55 and 75% RH.

The research indicates that local application of the top layer is less effective as it does not contribute to N. cucumeris to spread throughout the crop.

A practical test in a newly planted Alstroemeria crop with a full-field bran and yeast top layer was set up to study the long term survival of the mites and the effects on thrips control. It appears that other soil predatory mites have also been attracted by the top layer.

The research on top layers for Alstroemeria is part of the 'Masterplan Trips, a Public Private Cooperation’ (top sector T&U and various agricultural cooperatives).

Source: www.wageningenur.nl